Page 62 - Lab Manual & Project class 12

LABORATORY MANUAL CHEMISTRY
Oxalate is confirmed by the following tests:

(a) Acidify sodium carbonate extract with acetic acid and add calcium chloride
solution. A white precipitate of calcium oxalate, insoluble in ammonium
oxalate and oxalic acid solution indicates the presence of oxalate ion.
CaCl + Na C O 4 CaC O 4 + 2NaCl
2
2
2
2
Calcium oxalate
(White precipitate)
(b) KMnO test
4
Filter the precipitate from test (a). Add dil. H SO to it followed by dilute
4
2
KMnO solution and warm. Pink colour of KMnO is discharged:
4
4
CaC O + H SO CaSO + H C O
2 4 2 4 4 2 2 4
Maxbrain Chemistry
Calcium sulphate Oxalic acid
2 KMnO + 3H SO + 5H C O 2MnSO + K SO + 8H O + 10CO
4 2 4 2 2 4 4 2 4 2 2
Pass the gas evolved through lime water. A white precipitate is formed
which dissolves on passing the gas for some more time.

Step-III : Test for Sulphate and Phosphate

If no positive test is obtained in Steps-I and II, then tests for the presence of
sulphate and phosphate ions are performed. These tests are summarised in
Table 7.5.

Table 7.5 : Confirmatory tests for Sulphate and Phosphate

Ion Confirmatory Test

Sulphate ( SO 2– ) (a) Take 1 mL water extract of the salt in water or sodium
4 carbonate and after acidifying with dilute
hydrochloric acid add BaCl solution. White
2
precipitate insoluble in conc. HCl or conc. HNO is
3
obtained.
(b) Acidify the aqueous solution or sodium carbonate
extract with acetic acid and add lead acetate solution.
Appearance of white precipitate confirms the presence
2–
of SO ion.
4

Phosphate ( PO 3– ) (a) Acidify sodium carbonate extract or the solution of
4 the salt in water with conc. HNO and add ammonium
3
molybdate solution and heat to boiling. A canary
yellow precipitate is formed.

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24-04-2018